1. Field of the Invention
The present invention relates to a laser power control apparatus for controlling laser power in a combination drive which records information or reads recorded information on/from different types of optical disks by applying different laser lights onto the optical disks. More particularly, the present invention relates to a laser power control apparatus for controlling the laser power such that the different laser lights are collected by a common photodetector.
2. Description of the Background Art
In recent years, combination drives which are capable of reading recorded information or writing information using plural types of optical disks have been widely used. The combination drive may be generally represented by one that records and reproduces information on CDs and reproduces information on DVDs, as suggested in Japanese Patent Laid-Open Publication No. 2001-236726, for example. In such a combination drive, two lasers of different powers, a CD laser and a DVD laser, need to be controlled individually.
Referring to FIG. 17, a laser power control apparatus in a conventional combination drive will be described. A laser power control apparatus LP includes a CD laser power control system LPcd for controlling the power of a CD laser; a DVD laser power control system LPdvd for controlling the power of a DVD laser; and a controller 100 for controlling the operation of the entire laser power control apparatus LP.
The CD laser power control system LPcd includes an offset adjuster 1 (referred to as “Offset” in the drawing), an adder 20, a reproduction amplification unit Up, a recording amplification unit Ur, a laser drive circuit 7 (referred to as “LDD” in the drawing), a laser diode LD1, and a front monitor 8 (referred to as “PD” in the drawing). The laser drive circuit 7 allows the laser diode LD1 to emit CD laser light Lc having a predetermined amount of light, based on a reproduction laser drive control signal LDI1 supplied from the reproduction amplification unit Up or on a recording laser drive control signal LDI3 supplied from the recording amplification unit Ur.
The front monitor 8 is composed of a photodetector. The front monitor 8 collects the CD laser light Lc and generates a laser intensity signal PD01 having a voltage which is based on the amount of the light collected. The offset adjuster 1 adds a potential which corresponds to a predetermined offset value to the laser intensity signal PD01 through the adder 20, thereby generating an offset corrected laser intensity signal S1.
The reproduction amplification unit Up has a variable gain circuit 2p (referred to as “VGA” in the drawing), a sample/hold circuit 3p (referred to as “S/H” in the drawing), and an operational amplifier 4p. The variable gain circuit 2p functions so that the laser intensity signal S1 has a sufficient amplitude at reproduction, thereby generating a laser intensity signal S2p. The sample/hold circuit 3p samples and holds the laser intensity signal S2p at a predetermined timing, thereby generating a laser intensity signal S3p. The operational amplifier 4p compares between a reference potential Vp supplied from a variable voltage source 5p and the laser intensity signal S3p and then generates a reproduction laser drive control signal LDI1 based on the difference obtained from the comparison.
The recording amplification unit Ur has a variable gain circuit 2r, a sample/hold circuit 3r, an operational amplifier 4r, and a variable voltage source 5r, as does the reproduction amplification unit Up. The variable gain circuit 2r functions so that the laser intensity signal S1 has a sufficient amplitude at recording, thereby generating a laser intensity signal S2r. The sample/hold circuit 3r samples and holds the laser intensity signal S2r at a predetermined timing, thereby generating a laser intensity signal S3r. The operational amplifier 4r compares between a reference potential Vr supplied from a variable voltage source 5r and the laser intensity signal S3r and then generates a recording laser drive control signal LDI3 based on the difference obtained from the comparison.
Note that the reproduction amplification unit Up and the recording amplification unit Ur have basically the same configuration and function except that the reproduction laser drive control signal LDI1 and the recording laser drive control signal LDI3 generated by the reproduction amplification unit Up and the recording amplification unit Ur, respectively, have different levels. Therefore, the reproduction amplification unit Up and the recording amplification unit Ur are hereinafter collectively referred to as an “amplification unit U” as long as there is no particular problem. In addition, the variable gain circuits 2p and 2r are hereinafter collectively referred to as a “variable gain circuit 2”, the sample/hold circuits 3p and 3r referred to as a “sample/hold circuit 3”, the operational amplifiers 4p and 4r referred to as an “operational amplifier 4”, and the variable voltage sources 5p and 5r referred to as a “variable voltage source 5”. The reproduction laser drive control signal LDI1 and the recording laser drive control signal LDI3 are hereinafter collectively referred to as a “CD laser drive control signal LDIc”.
The DVD laser power control system LPdvd has an operational amplifier 6, a transistor PNP, a laser diode LD2, and a back monitor 19 (referred to as “PD” in the drawing). The transistor PNP allows the laser diode LD2 to emit DVD laser light Ld having a predetermined amount of light, based on a reproduction laser drive control signal LDI2 supplied from the operational amplifier 6. The back monitor 19 is composed of a photodetector, as is the front monitor 8. The back monitor 19 collects the DVD laser light Ld and generates a laser intensity signal PD02 having a voltage which is based on the amount of the light collected. The operational amplifier 6 compares the laser intensity signal PD02 to a reference signal PD2ref and then generates a reproduction laser drive control signal LDI2 based on the difference obtained from the comparison.
To the controller 100 a feedback signal Sf which indicates the operational conditions of the components of the laser power control apparatus LP is inputted from the laser power control apparatus LP. Further, to the controller 100 an operation mode signal Sm which indicates a user's instruction is inputted from the combination drive. The controller 100 generates a control signal Sc for controlling the operation of each component of the laser power control apparatus LP, based on the operation mode signal Sm and the feedback signal Sf.
As described above, in the conventional combination drive, the CD laser power control system LPcd and the DVD laser power control system LPdvd are independently configured, and thus a space-consuming photodetector is redundantly provided on each of the font and back monitors, which inhibits production of a small size combination drive.